While this typical configuration of the hollow chamber profile is applicable to all profile sizes employed, in practice, three different size groups have developed which can be classified by their covering width, i.e. by the effective slat width, determining the slat division in the closed shutter, as follows:
maxi-profiles having a covering width of about 52-55 mm PA1 standard profiles having a covering width of about 42 mm PA1 mini-profiles having a covering width of about 32-33 mm. PA1 (c) the radius of curvature of the outwardly convex main wall is 38.0 mm, with a tolerance of +4 mm,
The wider the covering width the larger the required dimension of the winding shaft diameter and the larger the outer diameter of the wound roller shutter. In housing conctruction, especially in the subsequent assembly and dissembly of roller shutters within the old buildings modernizing and reconstructing program, it is the mini-profile that is exclusively employed as it permits the use of winding shafts having diameters of as little as 40 mm.
The material to be considered for the roller shutter slat is extruded plastic material or roll-shaped curable plastic-formed aluminium strip material. The use of extruded plastic, admittedly, is comparatively low-priced permitting far-reaching liberties as to profile shaping; also, plastic roller-type shutters are less noisy in windy weather. However, the disadvantages exhibited by plastic material are the low degree of rigidity and an inadequate safety against burglary. Compared therewith, roller shutter slats of aluminium are substantially more expensive. However, by foaming them with, for example, polyurethane, they attain substantial rigidity. Hence, they cannot be readily forced open without applying substantial efforts and involving unreasonable noise.
The higher costs involved with aluminium slats, mainly, are due to the high material cost of the employed aluminium slats. With band thickness of 0.36-0.38 mm as commonly employed with the mini-profile, they exceed the costs of corresponding plastic, slats by 50 percent or more. Reduced slat, thicknesses would, therefore, be desirable for cost-saving reasons. However, in the profile dimensions developed for the mini-profile, this would involve an unsatisfactory decrease in rigidity both in the central hollow chamber area and on the hook and counter-hook.
Moreover, conventional hollow chamber profiles exhibit substantial difficulties in the event of extended shutter lengths of two meters or more as with doors. The resultant winding diameters require substantial cross-sections of the roller shutter casings which are deemed unsatisfactory especially with pre-assembled roller shutters.
It is the object of the invention to overcome the aforementioned disadvantages and provide a roller shutter slat of the above mentioned type which is made from roll-shaped aluminium strip and which, with a constant covering width within the above tolerance for the so-called mini-profile, can be manufactured at substantially lower cost, at the same time permitting a substantially reduced winding diameter in extended shutter length with no substantial loss in strength and rigidity as compared with the known roller shutter slats.